Question

Answer 1

Bài 3: 

Ta có: \(\left(2k-1\right)^2-9\)

\(=\left(2k-1-3\right)\left(2k-1+3\right)\)

\(=\left(2k-4\right)\left(2k+2\right)\)

\(=4\left(k-2\right)\left(k+1\right)⋮4\)